"So, my advice is take control from the start, don't let it degenerate into a free for all."
This is good advice. Although a well organised session should run itself, it does help to have someone at the helm. We've found that people like to be asked to perform. It does help when they are nervous, shy, or (usually unfounded), lacking in confidence. It also gives everyone a fair go. Someone could be wanting to play, but it can be difficult in a session once the diddly lot get going.